Why is Apple Watch indoor run distance inaccurate?
On a treadmill the watch has no GPS, so indoor distance is an estimate. Fix My Workout saves a corrected copy with the treadmill's distance.
Why indoor distance drifts
Outdoors, Apple Watch uses GPS. On a treadmill you stay in place, so it estimates distance from wrist motion, sensor data and earlier calibration. The estimate drifts in three common ways.
- Too short: less arm motion, holding the rails, or a stride that changes with incline.
- Too long: arm motion that does not match the belt speed.
- Off calibration: a recent outdoor calibration that does not match how you run on a treadmill.
How to correct the saved run
- Finish the workout on Apple Watch as usual.
- Open Fix My Workout on iPhone and select the Indoor Run or Indoor Walk.
- Enter the treadmill distance exactly as shown. Check the unit first: mixing miles and kilometres skews pace and weekly totals.
- Review the new pace and laps, save the corrected copy and check it in Fitness.
What happens after the fix
The corrected workout is a new entry in Apple Health; the original is not overwritten. Pace and laps change because they depend on the distance and the original timing. Heart rate and calories are carried across where Apple Health allows, not estimated from the new distance.
If you keep both entries, Fitness shows both workouts and your totals count both. Delete the inaccurate original once the copy looks right.
Calibration can improve over time, but treadmill estimates still vary. Treat the treadmill display as the reference and correct the saved workout when the difference matters.